The blockade has been imposed for about three years and, because it denies Gazans access to many goods, the so-called tunnel economy has thrived as Gazans seek to bring in materials from outside the strip.

The raids also follow a series of deaths in the occupied West Bank.

Two Palestinians were shot dead by Israeli troops near an army checkpoint close to the town of Nablus on Sunday.

Another two Palestinians died after apparently being shot by Israeli troops during violent protests in the city itself.

Medical workers say the dead were hit by live ammunition and an X-ray of one of the boys showed what appeared to be a bullet lodged in his head.

Israel has denied its troops used live ammunition and says it has launched an investigation.

Late on Monday, Israeli troops and Palestinian fighters exchanged gunfire near the Kissufim crossing point into the Gaza Strip, Israel's Channel 10 television reported.

'Friendly fire'

And in a separate incident an Israeli soldier was killed in a "friendly fire" incident near the border with Gaza, an army spokesman said.

The military said two groups of soldiers were tracking three Palestinian suspects who had crossed the security fence to the Israeli side when one group mistook the other soldiers for the Palestinians and fired.

The three Palestinians, who were not armed, were arrested.

Palestinians from the blockaded territory have been known to cross the fortified border in the same area in search of work in Israel.